The present invention relates to a voltage-tunable oscillator with a dielectric resonator.
It can be applied especially to the making of frequency synthesizers that can be used in radio transmitter/receiver stations working in frequency-hop mode.
Voltage-controlled oscillators conventionally comprise a dielectric resonator whose resonance frequency is fixed. This resonator is coupled with a diode, also called a varicap, whose capacitance varies according to a voltage level that is applied to it. This has the effect of modifying the tuning frequency of the oscillator continuously in a given frequency band.
One embodiment of an oscillator working according to this principle is described especially in an article by Mr. E. Hxc3xa9nicle, xe2x80x9cVCO Design Using Coaxial Resonatorsxe2x80x9d in the journal Trans-Tech Inc, November 1995.
In these oscillators the use of a varicap diode has the drawback of causing a drop in the Q factor of the resonator. This results in a deterioration of the phase noise.
The goal of the invention is to produce an oscillator that is voltage tunable in a wide range of frequencies without deterioration in the Q factor of the resonator.
To this end, an object of the invention is a voltage-controlled oscillator comprising a dielectric resonator, coupled to a load impedance through an active amplifier element characterized in that the dielectric resonator is made of a ferroelectric ceramic placed between two metallized surfaces and biased by an electric field created by a difference in potential applied between the two surfaces as a function of the tuning frequency of the oscillator.
An advantage of the invention is that it enables the application of a voltage control directly to the material forming the resonator without causing any deterioration in its Q factor. Through this principle, it becomes possible to produce a voltage-controlled oscillator having a characteristic phase noise of at least 20 dB in a very wide range of frequencies from the UHF wave bands to the microwave bands. This result cannot be achieved with the prior art oscillators controlled by varicap diodes.